Name: draft-martin-isis-local-protect-cap-01
Title: ISIS Extensions for Signaling Local Protection Capabilities
State: Active
Authors: Alia Atlas
Group: Individual Submissions (none)
Date: 2004-10-26
This document specifies additional information that can inserted in IS-IS
LSPs to convey link capabilities that may be useful in certain
applications. In particular, an IS may indicate that zero or more of its
links may be used by an upstream IS as an alternate, SPT-disjoint path to
an arbitrary destination D. Additionally, an IS may convey that zero or
more of its links are capable of breaking a U-turn, which may be described
as a single-hop forwarding loop between two IS's. This means that a router
can detect the presence of a forwarding loop by recognizing that traffic to
a destination is being received from a neighbor to which it has forwarding
state pointing back to the same neighbor for that destination. In such a
situation, it will switch to a loop-free node-protecting alternate until
new primary forwarding state has been installed, thus breaking the U-turn.
Therefore, the immediate applicability for these two link capabilities is
in support of local protection in the event of a link and/or node failure
while the IS-IS area is reconverging onto a new topology.
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